In general, a belt material from which a belt layer of a pneumatic tire is molded out is obtained in a manner that, after bias cutting a calendered material formed by pulling together and rubberizing a plurality of steel cords, cut-off pieces obtained thereby are joined to one another by making cut ends of the cut-out pieces to constitute both edges of the belt layer. On the other hand, belt layers of pneumatic tires differ in belt width and in cord angle from one another depending on specifications of the tires. Therefore, it is necessary to previously prepare various belt materials whose measurements are different by tire specification.
As a result, a large stock space for stocking the various belt materials becomes necessary in a conventional tire production facility. Additionally, since a belt layer processed in accordance with a particular tire specification cannot be diverted as a belt layer for another tire specification, there is a disadvantage that the materials come to be wasted because remains of the belt materials are generated in tire production processes. In addition, there is another disadvantage that quality degradation tends to occur because the cords are exposed when the belt material is cut along the cords. Furthermore, in a case where a wide variety of products in small quantities are produced, there is still another disadvantage that productivity is inferior because, when tire specifications are changed, there is a necessity to change drums around which lengthy belt materials are rolled up.
In response to these disadvantages, there has been proposed that a belt layer having desired measurements be formed by joining the strip pieces to one another in a manner that, while the strip pieces are tilted with respect to a circumferential direction of the tire, each of both sides of each strip piece is butted with one side of another stripe piece (refer to, for example, Patent Documents 1 and 2). Each of the strip pieces is formed of a plurality of steel cords pulled together and rubberized. In this case, inconveniences attributable to lengthy belt materials different by tire specification are resolved.
However, in a case where a belt layer of a pneumatic tire is composed of multiple strip pieces, while it is desirable that widths of the respective strip pieces be constant, it is difficult to butt-join an integer number of the strip pieces, which compose the belt layer, to one another around an entire circumference of the tire. That is, when the strip pieces are aligned in a circumferential direction of the tire, it leads to any overlap between the strip pieces unless a residual part of the strip pieces is cut off in a part of the belt layer in a circumferential direction of the tire. Additionally, even if the butt-joining could have been incidentally formed in any belt layer of the pneumatic tire, any overlap between the strip pieces can be caused in a part of another belt layer in a circumferential direction of the tire because this one has a circumferential length different from that of the first mentioned belt layer. Therein, the above-described overlap between the strip pieces can be a factor in deteriorating uniformity of the tire. On the other hand, in a case where a residual part of the strip pieces is cut off in order that the butt-joining can be ensured, quality degradation tends to occur because cords are exposed in cutting the strip pieces along the cords.
[Patent Document 1] Japanese patent application Kokoku publication No. Sho53-11723
[Patent Document 2] Japanese patent application Kokai publication No. Hei11-99564